Probing time-dependent afterslip and viscoelastic relaxation following the 2015 Mw7.8 Gorkha earthquake based on the 3-D finite-element model

Lina Su,Weijun Gan,Xiaoning Su,Fuqiang Shi,Junyi Yan

doi:10.1186/s40623-020-01296-x

Abstract

We analyzed daily displacement time series from 34 continuous GPS stations in Nepal and 5 continuous GPS stations in South Tibet, China, and extracted the first 4.8 years of postseismic motion after the 2015 Mw7.8 Gorkha earthquake. With the longer duration GPS observations, we find that postseismic displacements mainly exhibit southward and uplift motion. To study the postseismic afterslip and viscoelastic relaxation, we built a 3-D spherical finite-element model (FEM) with heterogeneous material properties and surface topography across the Himalayan range, accounting for the strong variations in material properties and surface elevation along the central Himalayan arc. On the basis of the FEM, we reveal that the predicted viscoelastic relaxation of cm level moves southward to the north of the Gorkha earthquake rupture, but in an opposite direction to the observed postseismic deformation in the south; the postseismic deformation excluding viscoelastic relaxation is well explained by afterslip downdip of the coseismic rupture. The afterslip is dominant during 4.8 years after the 2015 Mw7.8 Gorkha earthquake; the contribution by the viscoelastic relaxation gradually increases slightly. The lack of slip on a shallow portion and western segment of the MHT during and after the 2015 Gorkha earthquake implies continued seismic hazard in the future.

Highlights

On 25 April 2015, the Mw7.8 Gorkha earthquake struck, just 77 km northwest of Kathmandu, Nepal, resulting in large economic losses and a death toll of up to 8000 (Earthquake Relief Portal 2015)
Comparing the afterslip and viscoelastic relaxation predicted by our finite-element model (FEM) with afterslip by the SDM software (Wang 2013) and viscoelastic relaxation by the PSGRN/ PSCMP software (Wang et al 2006), respectively
S5 and S6), we find coherent patterns and equivalent magnitudes of afterslip and viscoelastic relaxation

Summary

Introduction

On 25 April 2015, the Mw7.8 Gorkha earthquake struck, just 77 km northwest of Kathmandu, Nepal, resulting in large economic losses and a death toll of up to 8000 (Earthquake Relief Portal 2015). The previous studies mostly employed the homogeneous elastic half-space or layered elastic model to explore afterslip (Sreejith et al 2016; Zhao et al 2017; Wang and Fialko 2018; Jiang et al 2018; Jiang et al 2019), and the layered model or lateral heterogeneous model, which incorporates a low viscous layer beneath the Tibetan Plateau to investigate viscoelastic relaxation (Zhao et al 2017; Wang and Fialko 2018; Jouanne et al 2019; Tian et al 2020)

Methods

Results

Discussion

Conclusion